Re: Weird qemu-nvmm problem

[Chavdar Ivanov <ci4ic4%gmail.com@localhost>]

On Thu, 12 Mar 2020 at 17:26, Andrew Doran <ad%netbsd.org@localhost> wrote:
>
> On Wed, Mar 11, 2020 at 06:45:06PM +0100, Maxime Villard wrote:
>
> > Please CC me for issues related to NVMM, there is a number of lists where
> > I'm not subscribed.
> >
> > My understanding is that this commit is the cause (CC ad@):
> >
> >       https://mail-index.netbsd.org/source-changes/2019/12/06/msg111617.html
> >
> > NVMM reschedules the thread when the SPCF_SHOULDYIELD flag is set. But
> > after this change the flag never gets set, so the rescheduling never
> > occurs, and NVMM is stuck with running the guest forever unless a signal
> > is caught in the emulator thread.
> >
> > The test program below shows the difference. On NetBSD-9 you have many
> > "resched", as expected. On NetBSD-current you have none.
> >
> > Andrew, can you have a look? There is a good dozen of places that use
> > SPCF_SHOULDYIELD for reschedulings, and they too may potentially be buggy
> > now.
>
> Yes that was incorrect and I have fixed it.  I will see about adding a
> wrapper function for this too.

On

NetBSD 9.99.49 (GENERIC) #0: Fri Mar 13 08:17:38 GMT 2020
        sysbuild@ymir:/home/sysbuild/amd64/obj/home/sysbuild/src/sys/arch/amd64/compile/GENERIC
my nvmm guests (which used to hang previously) appear to be working again.

>
> Andrew
>
> >
> > Thanks,
> > Maxime
> >
> >
> >
> > ---------------------------------------------------------------------------
> >
> > /*
> >  * # gcc -o test test.c -lnvmm
> >  * # ./test
> >  */
> >
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <unistd.h>
> > #include <sys/mman.h>
> > #include <fcntl.h>
> > #include <nvmm.h>
> > #include <stdint.h>
> > #include <string.h>
> >
> > int main()
> > {
> >       uint8_t instr[] = { 0xEB, 0xFE };
> >       struct nvmm_machine mach;
> >       struct nvmm_vcpu vcpu;
> >       uintptr_t hva;
> >
> >       nvmm_init();
> >       nvmm_machine_create(&mach);
> >       nvmm_vcpu_create(&mach, 0, &vcpu);
> >
> >       hva = (uintptr_t)mmap(NULL, 4096, PROT_READ|PROT_WRITE,
> >           MAP_ANON|MAP_PRIVATE, -1, 0);
> >       nvmm_hva_map(&mach, hva, 4096);
> >       nvmm_gpa_map(&mach, hva, 0xFFFF0000, 4096, PROT_READ|PROT_EXEC);
> >
> >       memcpy((void *)hva, instr, sizeof(instr));
> >
> >       nvmm_vcpu_getstate(&mach, &vcpu, NVMM_X64_STATE_GPRS);
> >       vcpu.state->gprs[NVMM_X64_GPR_RIP] = 0;
> >       nvmm_vcpu_setstate(&mach, &vcpu, NVMM_X64_STATE_GPRS);
> >
> >       while (1) {
> >               printf("looping\n");
> >               nvmm_vcpu_run(&mach, &vcpu);
> >
> >               switch (vcpu.exit->reason) {
> >               case NVMM_VCPU_EXIT_NONE:
> >                       printf("resched\n");
> >                       break;
> >               default:
> >                       printf("unknown: %d\n", vcpu.exit->reason);
> >                       break;
> >               }
> >       }
> > }



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